The present invention relates generally to microwave connectors. More particularly, the present invention relates to a microwave connector that connects to a microstrip circuit on a carrier and uses a glass bead for hermetic sealing.
FIG. 1 illustrates an assembly of typical connector components 1 along with a housing 2 containing a microstrip substrate 10 supported by a carrier 12. FIG. 2 shows more details of the connector components 1 and housing 2. FIG. 2 also illustrates a typical sparkplug type coaxial connector 18 and connector components 1 assembly. Components carried over from FIG. 1 to FIG. 2 are similarly labeled, as will be carried over in subsequent drawings.
The sparkplug type connector 18 includes a center conductor 16 with a female type pin which mates with a male pin 14 supported by the housing 2. The center conductor 16 of the connector 18 is supported by a glass bead 20. Surrounding the glass bead 20 is a metal cylindrical outer conducting shell 19 which is threaded like a sparkplug for insertion into a similarly threaded hole 22 in the wall of the package housing 2.
The center conductor 14 supported by the housing 2 is also supported by the glass bead 6 which is provided in a opening 22 of the housing. The glass bead 6 in the housing is further hermetically sealed using solder provided in the access hole 26 shown. The center conductor 14 extends a short distance onto the microstrip substrate 10.
The microstrip substrate 10 typically contains MMICs for mounting on the carrier 12. The carrier 12 is a thin piece of metal, typically xc2xd to 1 mm thick, which provides the ground for the microstrip substrate 10, and hence the MMICs on the microstrip substrate 10. Carriers which can provide grounding at high frequencies become more desirable with the increasing availability of MMIC subsystems. If a number of MMICs are mounted directly onto a housing and one of them fails, the entire assembly must be discarded, as it is generally impossible to remove a fragile MMIC after it has been mounted by soldering directly to the housing without destroying other MMICs in the vicinity. However, a carrier can be mechanically placed in and removed from the housing without destroying the circuit components mounted on it.
Conventionally, the connector components 1 provide for a coax to microstrip transition including electrical transition and impedance matching between the coaxial transmission line of the coaxial connector and the microstrip transmission line connected to the MMICs. As shown in FIG. 3, the compensation can include an air gap 40 between the support bead 6 and housing 2, as well as a controlled air gap 42 between the microstrip substrate and outer conductor formed by the housing 2. Typical dimensions for the compensation gaps are shown in FIG. 3 with a center conductor of 0.009xe2x80x3 and a center conductor pin 14 extending beyond the outer conductor 0.010xe2x80x3 onto the microstrip substrate 10.
As microwave components and subsystems go higher and higher in frequency, the importance of the coax connector becomes more critical. With the advent of multi-function MMIC chips, two factors normally not required at lower frequencies become required at higher frequencies. First hermicity, and second very short ground paths.
Hermicity in microwave packages is traditionally achieved by use of the glass beads. The beads themselves are hermetic and when soldered correctly into a package, the package becomes hermetic. For microwave applications, the areas surrounding the glass bead are critical for good RF performance. The tight tolerance compensation steps become difficult to achieve as the glass-beads get smaller in size at higher frequencies. The process of soldering the glass bead into the housing also becomes more critical and difficult as the beads shrink in size.
With MMICs built on carriers which are mounted on a housing, a long ground path gap 15 typically exists between the carrier 12 and the outer conductor 28 of the coaxial connector 1 joining the microstrip. The long ground path 15 results in poor performance of the coax to microstrip interface. FIG. 3 illustrates the typical performance of the connector connected to microstrip shown in FIGS. 1 and 2.
In accordance with the present invention, a hermetic glass bead and a grounding lip are incorporated into the connector, effectively eliminating the poor performance due to a long ground path. The glass bead forms both the hermetic seal and the support for the coax center conductor pin. The ground lip is in the required location to provide a short ground path for the connecting microstrip substrate. When the connector and the housing are coupled together, the assembly allows for a signal to efficiently pass through the center conductor pin to the microstrip line with an adequate ground. The user merely has to solder the connector into a very simple hole in the package. There is no need for soldering the glass bead into the connector, which at high frequencies is very difficult due to the small size of the glass bead. All compensation steps can further be incorporated into the connector.